Electrical submersible pumps (ESP) are often used to pump fluids from hydrocarbon wells. An ESP normally includes a motor, a pump, and a pressure equalizer or seal section that reduces a pressure differential between well fluid on the exterior and dielectric lubricant in the motor interior. A power cable extends from the wellhead to the motor to supply power. The power cable may be strapped to production tubing that supports the ESP, or it may be located within coiled tubing that supports the ESP.
A typical power cable has three copper conductors, each conductor surrounded by one or more layers of insulation, including heat resistant EPDM insulation. A jacket of oil resistant EPDM may encase the three conductors. An armor of galvanized or stainless steel formed in a strip wraps helically around the jacket.
If the power cable is to be used in wells that produce hydrogen sulfide gas, each conductor may have a sheath of lead. Each lead sheath serves as a barrier layer to prevent hydrogen sulfide gas from permeating under pressure through the insulation layers into contact with the copper conductors. If the gas reaches the copper conductors, it can corrode them. Also, when retrieving the ESP, if hydrogen sulfide gas has permeated through the insulation layers, the rapid decrease in well pressure can cause explosive decompression damage. While lead sheaths work well, they add weight to the power cable and cause environmental concerns during manufacturing.